Detecting computer security threats in electronic documents based on structure

ABSTRACT

In an embodiment, a method providing an improvement in remediating vulnerabilities in computer security comprising: receiving, using a network tap of a sensor computer that is coupled to a compromised computer, a communication packet that was sent from the compromised computer to a target computer; using the sensor computer, determining that the target computer is one of a plurality of enterprise computers; reading, at the sensor computer, a plurality of fields within a header of the communication packet; and performing a remediation measure by generating a header of an action packet, wherein the header comprises duplicates of at least some fields of the plurality of fields so as to appear to be generated by the target computer, generating a payload of the action packet, and sending the action packet comprising the generated header and the generated payload to the compromised computer.

CROSS-REFERENCE TO RELATED APPLICATIONS; BENEFIT CLAIM

This application claims the benefit under 35 U.S.C. § 120 as aContinuation of application Ser. No. 15/162,233, filed May 23, 2016,which is a Continuation of application Ser. No. 14/723,251, filed May27, 2015, now U.S. Pat. No. 9,350,757, the entire contents of which arehereby incorporated by reference as if fully set forth herein. Theapplicant(s) hereby rescind any disclaimer of claim scope in the parentapplication(s) or the prosecution history thereof and advise the USPTOthat the claims in this application may be broader than any claim in theparent application(s).

FIELD OF THE DISCLOSURE

The present disclosure generally relates to computer security techniquesapplicable to computers that have been compromised with bots and othermalware, and relates more specifically to techniques for remediating thesecurity threats using a distributed network of sensor computers.

BACKGROUND

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

In computer networking and security, a troublesome problem involves theinstallation, by attacker computers, of bots or other malicious software(“malware”) on unsuspecting computers (“compromised computers”) that arethen employed by the attacker to carry out attacks on a third computer,often associated with a business, enterprise, or other institution. Themode of attack in which the attacker takes control of a compromisedcomputer and uses it to initiate attacks on third computers can bedifficult for security experts to fully remediate because of problems inidentifying the ultimate attacker.

Present techniques to address the foregoing problem domain generallyhave been found to be ineffective, slow, or incomplete, so that improvedsolutions are needed.

SUMMARY

The appended claims may serve as a summary of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a computer networking environment featuring asecurity control computer and one or more sensor computers located nearcompromised computers;

FIG. 2A illustrates a process of inspecting web pages for securitythreats;

FIG. 2B illustrates other aspects of the process of FIG. 2A;

FIG. 3 illustrates an example of logical and functional elements of asensor computer;

FIG. 4 illustrates a first example of logical and functional elements ofinspecting logic;

FIG. 5 is a block diagram that illustrates a computer system upon whichan embodiment of the invention may be implemented;

FIG. 6 illustrates a distributed network of inspecting nodes;

FIG. 7 illustrates a second example of logical and functional elementsof inspecting logic;

FIG. 8 illustrates a computer networking environment featuring a sensorcomputer co-located with a compromised computer;

FIG. 9 illustrates a computer networking environment including anexample implementation of interface tap logic;

FIG. 10 illustrates a process of remediation of security threats.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however,that the present invention may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring thepresent invention.

Embodiments are described herein according to the following outline:

1.0 General Overview

2.0 Example Network Topology

3.0 Process Overview

4.0 Implementation Mechanisms—Hardware Overview

5.0 Remediation of Security Threats

6.0 Other Aspects of Disclosure

1.0 General Overview

In an embodiment, a data processing method providing an improvement incomputer security comprises selecting, from a queue identifying aplurality of web pages, a particular web page to retrieve from one of aplurality of internet sources; causing retrieving a copy of theparticular web page from a particular internet source; determining ahierarchical structure of the particular web page; based upon ahierarchical structure of the particular web page and withoutconsideration of content of the particular web page, identifying one ormore features, of links in the particular web page or files referencedin the particular web page, that indicate one or more security threats;determining a reputation score for the particular web page; determininga specified remediation measure, based upon the reputation score, toremediate a security threat that is identified in the particular webpage; providing the specified remediation measure to one or more of acompromised computer, a sensor computer and an enterprise computer.

In an embodiment, a data processing system comprises a plurality ofsensor computers, each of which is coupled to different one among aplurality of compromised computers in geographically distributedlocations, each of the compromised computers comprising at least onemalware item that is configured to direct unauthorized network activitytoward one or more enterprise networks or enterprise computers, whereinthe compromised computers are logically between one or more attackercomputers and the one or more enterprise networks or enterprisecomputers; a security control computer that is coupled to the sensorcomputers and configured with security logic which is configured whenexecuted to perform: obtaining, from the sensor computers, detectiondata relating to network messages that the compromised computers emit,as the compromised computers emit the network messages; using thedetection data, identifying one or more security threats that areindicated by the network messages; determining a specified remediationmeasure to remediate one or more of the security threats; providing thespecified remediation measure to one or more of the compromisedcomputer, the sensor computer and an enterprise computer.

In another embodiment, a data processing system providing an improvementin computer security comprises a plurality of sensor computers, each ofwhich is coupled to different one among a plurality of compromisedcomputers in geographically distributed locations, each of thecompromised computers comprising at least one malware item that isconfigured to direct unauthorized network activity toward one or moreenterprise networks or enterprise computers, wherein the compromisedcomputers are logically between one or more attacker computers and theone or more enterprise networks or enterprise computers; a securitycontrol computer that is coupled to the sensor computers; one or morenon-transitory data storage media in the security control computerstoring security logic comprising one or more sequences of instructionswhich when executed cause the security control computer to perform:selecting, from a queue identifying a plurality of web pages, aparticular web page to retrieve from one of a plurality of internetsources; causing retrieving a copy of the particular web page from aparticular internet source; determining a hierarchical structure of theparticular web page; based upon a hierarchical structure of theparticular web page and without consideration of content of theparticular web page, identifying one or more features, of links in theparticular web page or files referenced in the particular web page, thatindicate one or more security threats; determining a reputation scorefor the particular web page; determining a specified remediationmeasure, based upon the reputation score, to remediate a security threatthat is identified in the particular web page; providing the specifiedremediation measure to one or more of a compromised computer, a sensorcomputer and an enterprise computer.

The mode of attack in which the attacker takes control of a compromisedcomputer and uses it to initiate attacks on third computers can bedifficult for security experts to fully remediate because of problems inidentifying the ultimate attacker. When the attacker computer is locatedbehind a firewall, or owned and operated by a malicious state actor, itmay be practically impossible to identify the true actor. Further, theowner or operator of the compromised computer may be unaware that themalware is present on the system or used to initiate attacks againstothers. However, the target of the attack—such as a businessenterprise—often can determine that it is under attack, and often cantrace the source of the attack to a compromised computer. Withinformation about the location of compromised computers, the techniquesdescribed herein can be deployed to provide effective means to blockattacks on the enterprise computer and, additionally or alternatively,to remediate the compromised computers.

While each of the drawing figures illustrates a particular embodimentfor purposes of illustrating a clear example, other embodiments mayomit, add to, reorder, and/or modify any of the elements shown in thedrawing figures.

2.0 Example Network Environment

FIG. 1 illustrates a computer networking environment featuring asecurity control computer and one or more sensor computers located nearcompromised computers; FIG. 3 illustrates an example of logical andfunctional elements of a sensor computer; FIG. 4 illustrates a firstexample of logical and functional elements of inspecting logic; FIG. 6illustrates a distributed network of inspecting nodes; FIG. 7illustrates a second example of logical and functional elements ofinspecting logic.

Referring first to FIG. 1, in one embodiment, a networked environmentmay have as principal elements an attacker computer 102 coupled to anetwork 104, a compromised computer 104, a sensor computer 110, anenterprise computer 112, and a security control computer 120. Attackercomputer 102 may be any computer that is ultimately used to initiate anattack, or the distribution of bots, other malware or viruses, and maybe located within the same geographic region as other elements of FIG. 1or in a different region. The attacker computer 102 may be used by,owned by, operated by, or located within a malicious state actor, suchas within one of several countries of the world that are regularlyassociated with initiation of attacks apparently on behalf of thegovernment or military organization of those states, but the presence ofa state actor in the networked environment of FIG. 1 is not required inall embodiments.

Network 104 comprises one or more local networks, wide area networks,and/or internetworks and may comprise the public internet in whole or inpart. In an embodiment, the compromised computer 106 hosts or executesmalware 108 that was previously obtained from or installed by theattacker computer 102 as indicated by a broken line in FIG. 1 indicatinga logical connection of the attacker computer to the compromisedcomputer. The compromised computer 106 may be coupled to network 104indirectly through a firewall 109 that is typically co-located with thecompromised computer. The compromised computer 106 also may host abrowser, as further described herein. The compromised computer 106 maybe a server computer of an enterprise that services file requests orserves web pages to one or more users of the enterprise. Thus,compromised computer 106 may broadly represent two or more computerswithin an enterprise, one or more of which is compromised, and/or one ormore of which accesses or uses the computer for another purpose.

In an embodiment, sensor computer 110 is deployed physically near or atleast in the same LAN segment as the compromised computer 106 andlogically behind the firewall 109. Sensor computer 110 is coupled tocompromised computer 106, and/or firewall 109, and configured as anetwork tap to enable the sensor computer to receive and inspect allpackets or other data communications that the compromised computer sendsor receives. For example, sensor computer 110 is configured to obtaincopies of all packets arriving from network 104 and directed to thecompromised computer 106 on any interface of the compromised computer,and originating from the attacker computer, a third party web site, orany other data source. Typically the sensor computer 110 obtains packetsfrom the compromised computer 106 in a transparent manner withoutaffecting transit of the packets; however, as described further herein,the sensor computer also may be configured to reconfigure the firewall109 to block transmission of certain packets, and/or to queue orotherwise prevent transit of packets in a form of packet shoot-down.

In an embodiment, as sensor computer 110 receives and inspects packetsdirected to the compromised computer 106, the sensor computer createsand stores sensor data 111 that describes aspects of the packets,attacks, or related metadata. In an embodiment, the sensor data 111 islocally stored at the sensor computer and periodically forwarded to thesecurity control computer 120; for example, the sensor computer mayserve as a local cache that is periodically flushed to the securitycontrol computer for persistent storage in one of the databases 140,142.

The sensor computer 110 typically is used, owned and operated by anentity different than that of compromised computer 106; for example, thesensor computer may be owned or operated by a security organization orenterprise that also owns, operates or uses the security controlcomputer 120, as indicated by a broken line in FIG. 1 indicating alogical connection between sensor computer 110 and security controlcomputer 120.

Placement of sensor computers 110 may be performed by identifyingmalicious activity at a central location and tracing the activity to aparticular compromised computer, then contacting the owner of thatcomputer and reaching an agreement to place a sensor computer 110coupled to that compromised computer. For example, the owner could bepaid a research fee to permit local inspection of traffic to or from thecompromised computer. The identification may use a variety of techniquesincluding following malicious traffic from an available computer towardother computers that are compromised without the knowledge of theirowners or operators, seed programs, malware reverse-engineering, and soforth.

Functions of sensor computers 110 generally may include filtering onports of interest such as remote desktop protocol; RTP; SSL; SFTP; FTP;and others; detecting when message output or packet output reaches acertain capacity; detecting session construction for sessions with othercomputers; and analysis of intervals of times of day when messages aresent or when certain ports are used in packets. In all these examples,passive monitoring of traffic on ports is performed, data is storedlocally on the sensor computer 110 and then periodically data is sent inreports to the security control computer. The data also can befingerprinted to create signatures of observed packet patterns. Datacollection at sensor computers 110 also may comprise collectingusernames or e-mail addresses from phishing emails that a particularuser clicks through; the username can be used to more finely correlate aparticular bad set of data with a particular user, rather than aparticular machine.

For the purpose of illustrating a clear example, FIG. 1 shows a singlesensor computer 110 coupled to a single compromised computer 106.However, in other embodiments, there may be any number of sensorcomputers 110 deployed in geographically distributed locations andassociated with many different compromised computers that are owned andoperated by different parties. Thus, this disclosure specificallycontemplates the deployment of a large, widespread, geographicallydistributed overlay network consisting of large numbers of sensorcomputers 110, all reporting data to and interoperating with one or moresecurity control computers 120 that manage and control the sensorcomputers, where each of the sensor computers is co-located with adifferent compromised computer in a different location. The compromisedcomputers may be owned by, operated by, or used by completely differentand unrelated companies, enterprises, institutions or other parties, andmay have been compromised by any number of different attacker computers102 at different times. Additionally or alternatively, two or more ofthe compromised computers may be at the same physical location or in thesame general geographic region, such as a store, campus or territory,and coupled to a single sensor computer 110 or multiple different sensorcomputers.

In an embodiment, network 104 also is coupled through an enterprisefirewall 113 to the enterprise computer 112. Because the enterprisecomputer 112 is coupled to the network 104, the malware 108 incompromised computer 106 may initiate one or more attacks on theenterprise computer, as indicated by a broken line in FIG. 1 indicatinga logical connection between the malware and the enterprise computer.Attacks on enterprise computer 112 may include any known form ofcomputer attack, intrusion or investigation that is now know, orequivalents thereof, including but not limited to: denial or service(DoS) attacks; installation of viruses, spam or adware; passwordharvesting.

In an embodiment, security control computer 120 comprises inspectinglogic 122, enrichment logic 124, identity logic 126, sensor logic 128,remediation logic 130, presentation logic 132, and one or more databaseinterfaces 134 that are coupled to one or more databases 140, 142. Whileeach of the components listed above are illustrated as separate, inother embodiments one or more of the components listed above may be partof and/or executed using the same logic. The general configuration andfunctions of the logical elements of security control computer 120include:

-   -   inspecting logic 122: determining web pages to inspect for        security threats; loading the web pages using a headless HTTP        browser or the equivalent; analyzing the structure of the web        pages independent of content and inspecting links and page        references in the structure; determining a reputation score and        remediation measures for the web pages;    -   enrichment logic 124: querying one or more enrichment data        sources 150 to obtain other information about web pages for the        purpose of assisting the identification of threats and the        determination of a reputation for the web pages;    -   identity logic 126: determining the identity of apparent        attackers, based upon analysis of advertising network        information, packets obtained from the sensor computer 110 or        the enrichment sources; determining the identity of other        compromised computers that may need investigation or the        installation of other sensor computers;    -   sensor logic 128: interfacing to one or more of the sensor        computers 110 to obtain sensor data 111 that is gathered and/or        formed at the sensor computers and to provide the sensor data to        other elements of the security control system or to databases        140, 142;    -   remediation logic 130: determining one or more remediation        measures to implement via sensor computer 110 on firewall 109 or        compromised computer 106, or on enterprise computer 112;        distributing the remediation measures in the form of        instructions or configuration data to any of the firewall,        compromised computer, or enterprise computer;    -   presentation logic 132: forming one or more reports, graphs, or        charts that report, explain, describe, show, aggregate or        otherwise display the sensor data 111 and/or other information        about security threats and remediation measures. For example,        the open source project SPARK may be used to create graphs for        visualization of links between nodes and associations of malware        to links or nodes, with or without identification of people and        machines that intersect with the links and nodes;    -   database interfaces 134: managing transfer of data to one or        more databases 140, 142.

In an embodiment, databases 140, 142 comprise one or more of a domainreputation score database and a binary data warehouse. In oneembodiment, the databases may be implemented using the CASSANDRA and/orHDFS open source projects. In various embodiments, the enrichmentsources 150 may comprise global user browsing data indicating which websites and web pages users are browsing on a global basis, reputationdatabases accessible through network requests, or other sources ofmetadata about security threats, web sites, or web pages.

In an embodiment, one or more advertising exchange networks 160 arecommunicatively coupled to security control computer and provideadvertisement exchange network data that identifies computers and/orusers based upon the delivery of advertisements through the networks tothose computers, and other sources; this data may be consumed by theidentity logic 126 to identify computers that may need inspection orthat may need remediation.

The identity logic 126 may be configured to interface with theadvertising exchange networks 160 for the purpose of identifying usersor computers by listening on advertising exchanges for bids onadvertisements. As an example, a website may serve varyingadvertisements based on interoperation with the advertising exchangenetworks 160 so that when a user computer requests a webpage, thatrequest appears in the ad exchange and an algorithm considers availablebids to determine which ad to serve in response to the request. Therequest may include all available demographic data and machine-relateddata based upon cookies on the user machine, browser fingerprint, typeof site visited, or other sources such as account information. In anembodiment, the security control computer 120 is configured to alwaysbid the lowest amount to the advertising exchange networks 160, whichcauses the networks to provide receive updates to the control computerof data for all other bids that are higher, and enables the controlcomputer to receive the same demographic data about the user computer oraccount. Typically the data for a bid event includes: Cookie, IP from,destination, browser details, destination URL, time.

While these responses of the advertising exchange networks 160 normallyare intended to enable a receiving computer to determine whether to bidhigher, based upon information about who or what computer will receivean advertisement, in an embodiment, the security control computer 120never bids higher but receives and uses the data for security purposes.For example, receiving such user profile data or computer profile datafrom the advertising exchange networks 160 effectively informs thesecurity control computer 120 that a particular computer, or at least aprofile of data about the computer in association with an IP address,visited a particular website, when, and where the user linked to thesite from. This data may be correlated to stored mappings of IPaddresses to particular companies or entities. Based on such mappings,the security control computer 120 can determine that the particular userat the company browsed to the particular website, which may be useful inremediation.

A “computer” may be one or more physical computers, virtual computers,and/or computing devices. As an example, a computer may be one or moreserver computers, cloud-based computers, cloud-based cluster ofcomputers, virtual machine instances or virtual machine computingelements such as virtual processors, storage and memory, data centers,storage devices, desktop computers, laptop computers, mobile devices,and/or any other special-purpose computing devices. Any reference to “acomputer” herein may mean one or more computers, unless expressly statedotherwise.

A browser may be one or more computer programs or other softwareelements stored in electronic digital memory and executed on a computerthat receives instructions from a server computer, performs one or moreof the received instructions, causes to display content, provides a userinterface (“UP”) to receive user inputs, and/or receives and responds toone or more inputs from a user based on or according to the one or moreperformed instructions. A browser and/or components of a browser may beimplemented into an application. For example, a browser and/orcomponents of a browser may be implemented into a standalone, web-based,and/or mobile application as part of a web view, and/or web viewcontroller, to send and/or receive data over HTTP, SPDY, and/or otherprotocol(s). A user may use a browser to send data to a server computer.The server computer may respond with additional instructions.

A page or web page may be a set of instructions that define one or moreobjects and/or operations that may be executed concurrently and may bevisually displayed together. For example, in response to a request froma client computer, a “home page” may be sent to the client computer. Thehome page may be a set of instructions that a web server sends to aremote client computer if no parameters are included in the request. Onepage may reference and/or include other pages. For example, in responseto a user selecting a link in a current page through a browser, thebrowser may request and receive a partial page. The partial page may bedisplayed in the interface currently displayed and defined by thecurrent page.

An object may be a data structure that can be identified by anidentifier and/or a relationship with another object, such as a link,form, button, image, field, input, and/or sub-page. For example, anobject may have a unique identifier, which can be used to reference theobject. An object may also be referenced by its position in a hierarchyof object.

An object may have one or more identifiers. For example, a link may beidentified by a particular attribute in the link, such as a “name”,“id”, or “class” attribute. A link may be identified by an object thatincludes the link. For example, each link a division or section of apage may be identified by the division or section's identifier. Also forexample, each link in a source page may be identified by the identifierfor the source page, such as the uniform resource locator (URL) of thesource page. One or more links may be identified by a target page. Forexample, each link in any page may be identified by the target page thatthe link points to. Additionally or alternatively, links may beidentified by a combination of identifiers.

An attribute may be data that identifies and/or describes theappearance, behavior, and/or content of an object. For example, anattribute may be a unique identifier, such as a name. An attribute mayindicate that an object is a type of text field, text area, checkbox,and/or radio button. Other attributes may define or describe dimension,position, color, visibility, value, and any other functional or visualaspect of an object.

A link may be an object that references a page or web page. The pagereferenced by the link may be referred to as a target page. A link mayreference a target page by including a URL and/or other data thatidentifies a target page. A link may comprise one or more parameters.Additionally or alternatively, a link may comprise logic and/orinstructions that are executed when the link is selected. Additionallyor alternatively, a link may comprise and/or reference one or moreobjects that gather data and submit the data to a web server. Forexample, a link may reference a form. After data is entered into theform, and the link is selected, a request for a target page may be sentand the data in the form may be submitted with the request. The targetpage may comprise an error and/or success code. A target page need notinclude HTML, CSS, and JavaScript. Also for example, a link may comprisea form that references a target page. After data is entered into theform, and a submit button is selected, a request for the target page maybe sent and the data in the form may be submitted with the request.

A link may be included in a page. The page the link is included in maybe referred to as the source page. Additionally or alternatively, a linkmay be included in a short messaging service “text” message, instantmessage, email, and/or other medium.

In an embodiment, each of the functional units of security controlcomputer 120 and sensor computer 110 may be implemented using any of thetechniques further described herein in connection with FIG. 5; forexample, the security control computer 120 may comprise ageneral-purpose computer configured with one or more stored programswhich when executed cause performing the functions described herein forthe intermediary computer, or a special-purpose computer with digitallogic that is configured to execute the functions, or digital logic thatis used in other computing devices.

Referring now to FIG. 3, in one embodiment, an example of logical andfunctional elements of a sensor computer 110 may comprise interface taplogic 304, which is coupled to port filter logic 306, capacity detectionlogic 308, and message timing analysis logic 310. Sensor computer 110also may comprise analysis and reporting logic 312 that is coupled tooutputs of the port filter logic 306, capacity detection logic 308, andmessage timing analysis logic 310. In one embodiment, the interface taplogic 304 is coupled to one or more network interfaces 302 of thecompromised computer 106 and configured to transparently orpromiscuously receive copies of packets that arrive at the networkinterfaces from other sources.

In this configuration, the interface tap logic 304 may obtain copies ofthe packets and queue them for inspection by one or more of the portfilter logic 306, capacity detection logic 308, and message timinganalysis logic 310 without otherwise affecting transit or forwarding ofthe packets to or within the compromised computer. This approach permitsaltering data flow to an enterprise computer while packets emitted fromthe compromised computer are inspected.

In an embodiment, port filter logic 306 is configured to filter thereceived packets on particular ports of interest; that is, the portfilter logic drops or ignores all packets that do not include, in theTCP/IP 5-tuple for example, one of a set of particular port values thatare often associated with attacks. Examples include port values forremote desktop protocol; RTP; SSL; SFTP; FTP. In an embodiment, thecapacity detection logic 308 is configured to detect when the sensorcomputer 110 is sending a number of outbound packets toward enterprisecomputer 112, or toward other destinations, which exceeds a specifiedthreshold that is associated with an attack vector. That is, certainattacks are known to be associated with causing a compromised computerto emit a large number of spurious, malicious, useless or unnecessarypackets, and the capacity detection logic 308 is configured to determinewhen conditions indicate that an unreasonable number of packets is sent.

In an embodiment, the message timing analysis logic 310 is configured todetect when packets are sent at unreasonable times. For example, theremay be bots or malware that is dormant during daylight hours butsuddenly starts sending a flood of DoS packets, or other traffic, at3:00 AM or other times during which computer usage is typically low.Configuration data associated with the message timing analysis logic 310may vary operation and the detection of attacks according to a localenvironment, user base or context. For example, in hospitals, lawenforcement, or other environments it may be reasonable for largetraffic volume to occur at different times.

In an embodiment, analysis and reporting logic 312 is configured toperform local analysis of packets of interest, to detect potentialattacks or packets of interest, and to provide reports of the analysis,or raw data, to the sensor logic 128 at security control computer 120.For example, the analysis and reporting logic 312 may manageperiodically forwarding the sensor data 111 to the security controlcomputer 120 as previously described.

In one embodiment, a function of the system of FIG. 1 is to inspect alarge number of web pages and/or other electronic documents that arehosted in sources that are capable of browsing via network 104, toidentify security threats represented in the web pages or documentsand/or a security reputation of the web pages or documents, and to useinformation about the security threats to determine remediation measuresthat may be directed to one or more of the firewall 109, compromisedcomputer 106, and enterprise computer 112. In an embodiment, inspectingweb pages as described herein may encompass a large number of web pages,and even all web pages that are capable of browsing using the publicinternet. However, embodiments are not concerned with crawling,analyzing, or indexing the content of web pages or electronic documents;instead, the goal of inspection is to identify links and file referencesin the web pages, based upon web page structure independent of content.Thus, embodiments contemplate the implementation of a form of webbrowsing that is capable of operations which, given sufficient computingresources and time, are capable of identifying all possible securitythreats in all possible web pages based upon page structure, links andfiles and without regard to indexing substantive content such as text,images, links or files. While links or files are considered in theinspection operations and analysis, they do not need to be indexed;rather, they are used to develop reputation and threat information forstorage in association with identifiers of pages.

Turning to FIG. 4, a first example of logical and functional elements ofinspecting logic is shown. In the embodiment of FIG. 4, inspecting logic122 of security control computer 120 (FIG. 1) may comprise frontiermanager logic 402 that is coupled to provide output to fetching logic404 and to receive input from scheduling logic 410, as well as analysislogic 406 that is coupled to receive input from fetching logic 404 andfrom structural change detection logic 408 and to provide output todatabase interface 134 for updating the databases 140, 142.

In an embodiment, in operation, frontier manager logic 402 is configuredto determine the next web page to retrieve based upon any of severalcriteria such as links obtained from a prior page and timing. Forexample, in one embodiment input is received from scheduling logic 410to determine whether a particular web page may be obtained from aparticular web server or to adjust the timing of successive requests fordifferent web pages from the same web server to prevent triggeringthrottling or other blocking efforts at the web server. In anembodiment, once the frontier manager logic 402 has determined which webpage to retrieve and determined a time or schedule for retrieval, thefrontier manager logic signals the fetching logic 404 to fetch thespecified web page.

In an embodiment, if fetching logic 404 successfully retrieves a copy ofa web page or other electronic document from a network resource, thefetching logic signals the analysis logic 406 to perform analysis of thepage or document. In an embodiment, the analysis logic 406 generally isconfigured to compute a fingerprint such as a hash value for the webpage, to determine a structural form of the web page, to traverse linksin the web page, and to analyze file references in the web page, usingtechniques that are further described herein, in section 3 for example.In an embodiment, analysis logic 406 receives input from structuralchange detection logic 408 indicating whether a current structure of theweb page is the same or different than the structure of the same webpage as observed after a previous browsing or retrieval operation. Theanalysis logic 406 also is configured to store, via database interface134 and using the databases 140, 142, the fingerprint value for the webpage in association with a URL or other identifier, metadata describingthe web page structure, reputation values, and information relating tothreats, malware or attacks.

In an embodiment, analysis logic 406 also has an output path thatprovides input to frontier manager logic 402. In this configuration,inspecting logic 122 incorporates a feedback loop with which theanalysis logic 406 may influence the frontier manager logic 402 withrespect to the selection of the next web page for analysis. For example,the analysis logic 406 may determine that a set of links in the webpage, if traversed, would result in an endless loop of redirection orretrieval operations that would effectively render operation of thefetching logic 404 impractical or impossible; in response, the analysislogic may instruct the frontier manager logic 402 that the set of linksis “bad” and should be excluded from future fetching operations.

In one embodiment, the inspecting logic 122 may be implemented using aplurality of related but independently executed processing nodes. FIG. 6illustrates a distributed network of inspecting nodes, in one exampleembodiment. A plurality of inspecting nodes 602 are coupled to oneanother in a fully meshed network. In one approach, each of theinspecting nodes 602 implements the inspecting logic 122 as previouslydescribed, executes in parallel with all other inspecting nodes, andoperates with respect to a discrete and distinct set of web pages, linksand/or files.

In one mode of operation, when a first inspecting node 602 identifies anew link in a web page that has been fetched, the first inspecting nodedetermines, based upon a hash value of the link, which of the otherinspecting nodes is responsible for processing that link or a web pagelocated at that link. In an embodiment, the value space or hash space ofall the hash values is segmented among the inspecting nodes 602 so thata particular range or segment of hash values is uniquely associated witha particular inspecting node. Therefore, a particular hash value alwaysmaps to the correct inspecting node that has responsibility forprocessing links within its mapped range of hash values. Consequently,determining a hash value for a link can result in rapid distribution ofthe link to a particular one of the inspecting nodes 602 for processing.

Moreover, there is no need to define lists of domains, networkaddresses, or other identifiers of web sites, domains, web pages, linksand/or files for which each different inspecting node 602 hasresponsibility for processing. Instead, each of the inspecting nodes 602can determine automatically, based upon a hash value or the equivalentfor domains, network addresses, or other identifiers of web sites,domains, web pages, links and/or files, and a mapping of ranges of thevalue space to different ones of the inspecting nodes 602, which eachdifferent inspecting node 602 has responsibility for processing.Further, in response to identifying a new web page, link, or file, aninspecting node 602 may match an identifier to its local list beforedetermining to pass the a new web page, link, or file to a differentinspecting node 602.

FIG. 7 illustrates a second example of logical and functional elementsof inspecting logic 122. In the embodiment of FIG. 7, a URL in-box 702stores a queue of URLs representing the next web pages to browse andinspect. The URL in-box 702 is coupled to domain & URL prioritizationlogic 704, which is configured to periodically inspect the URL in-boxand determine which domain(s) or URL(s) should be given differentpriority values; for example, associating a higher priority value with aparticular URL effectively results in scheduling that particular URL forretrieval and inspection sooner. The domain & URL prioritization logic704 may determine a priority value for a particular URL in whole or inpart by retrieving a reputation value from a domain reputation scoredatabase 706, based upon the URL or a hash of the URL. In variousembodiments, the database 706 may be one of the databases 140, 142, ormay be part of one of the enrichment sources 150.

In an embodiment, a robots directive analysis unit 708 is coupled to thedomain & URL prioritization logic 704 and to a plurality of robots.txtfetcher units 710, of which any number may be instantiated in variousembodiments or execution scenarios. The robots directive analysis unit708 is configured to request one of the fetcher units 710 to retrievethe “robots.txt” file from the web server associated with the next URLthat has been assigned top priority in the URL in-box 702. In responseto successfully retrieving the “robots.txt” file for a particular webserver, the robots directive analysis unit 708 reads text of the file todetermine how the target web server will respond to automated retrievalof pages at the website. Based upon this analysis, the robots directiveanalysis unit 708 instructs a politeness management unit 712 how toconfigure a delay queue coupled to the politeness management unit toorder, manage or otherwise queue one or more particular web pages forretrieval from the same web server from which the “robots.txt” file wasobtained. As a result, web pages will be retrieved from a particular webserver without violating the directives in the “robots.txt” file, sothat the inspecting logic 122 is not throttled or blocked by the targetweb server.

A plurality of page fetch spiders 716 are coupled to the politenessmanagement unit 712. In one embodiment, the politeness management unit712 periodically removes a URL from the delay queue 714 and passes it toan available page fetch spider 716, with a signal to retrieve the webpage at the specified URL. If no page fetch spider 716 is available,then the politeness management unit 712 may instantiate another pagefetch spider, subject to the amount of available computing resourcessuch as memory and CPU.

Each page fetch spider 716 is configured to retrieve an HTML filerepresenting a web page using the URL with which it was provided by thepoliteness management unit 712, and to provide a copy of the HTML file,or a handle identifying a memory or disk location of the HTML file, to abinary analysis manager 720 and a page analysis manager 730. In anembodiment, the binary analysis manager 720 is configured to analyze anddetermine reputation and threats associated with binary data sourcessuch as executable files referenced within a web page, and the pageanalysis manager 730 is configured to analyze a page structure of theweb page, independent of content, to identify links or files for furtherinspection or retrieval.

As seen in FIG. 7, each of binary analysis manager 720 and page analysismanager 730 is configured with a downstream pipeline comprising aplurality of processing units that may execute in parallel with respectto the same target web page that is undergoing inspection. Turning firstto binary analysis manager 720, in one embodiment output from the binaryanalysis manager is coupled to one or more binary analyzer units 722,any number of which may be instantiated. The binary analysis manager maydistribute identifiers of binaries of a particular web page to any oneof the binary analyzer units based upon various load-sharing techniquessuch as round-robin distribution or size of the binary.

In an embodiment, output from each of the binary analyzer units 722 iscoupled to a binary analysis aggregator 724 that receives and aggregatesresults of the analysis. For example, a first binary analysis unit 722may analyze a first binary that is referenced in a particular web page,and a second binary analysis unit 722 may analyze a second binary thatis referenced in the same particular web page, resulting in differentreputation or threat scores for the two different binaries. In response,binary analysis aggregator 724 may determine an aggregated score for allbinaries referenced in the particular web page. Aggregation may usearithmetic averaging, weighted scoring based upon the size of the binaryor the domain reputation score that was earlier obtained from database706, or other approaches. The resulting aggregated score value isprovided to binary data warehouse 726, where the aggregated score valueis stored in a record of a database table in association with anidentifier of the binaries and/or an identifier of the web page.

Turning now to the page analysis manager 730, in one embodiment aplurality of page analyzer units 732 are coupled to the page analysismanager, which distributes one or more HTML documents, or handles orother references of locations in memory or disk for the HTML documents,to the page analyzer units. The page analysis manager 730 may distributeidentifiers of a particular web page to any one of the page analyzerunits 732 based upon various load-sharing techniques such as round-robindistribution or size of the web page.

Each page analyzer 732 is configured to perform structure-based analysisof the web page that was retrieved. In one approach, a document objectmodel (DOM) tree structure of the web page is determined and thesubstantive content of the web page in terms of text, images or otherelements is not considered. Analysis of DOM structure may includedetermining the number of links, the number of redirection operationsthat are triggered by traversing each link, whether the DOM structurehas changed since a last retrieval of the same web page, or otherfactors. These analysis operations may result in generating a reputationscore for the web page reflecting a likelihood that the web page conveysmalware, contains script code to execute malicious operations, orotherwise represents a security threat.

In an embodiment, each page analyzer 732 provides output of theanalysis, in terms of the reputation score of links and/or files in thepage, and a set of other links to traverse to inspect other web pages,to a page analysis aggregator 734. In response, binary analysisaggregator 734 may determine an aggregated score for the web pagestructure, and an aggregated set of other links to traverse, based uponresults of the individual page analyzer units inspecting the particularweb page. Aggregation may use summation or concatenation for sets oflinks, and for reputation may use arithmetic averaging, weighted scoringbased upon the size of the web page structure or the domain reputationscore that was earlier obtained from database 706, or other approaches.

The resulting aggregated data is provided to distribution manager 736.In one embodiment, the distribution manager 736 is configured to providethe analysis data to one or more of two locations: the URL in-box 702,and/or one or more remote in-boxes 750. When the analysis data isprovided to the URL in-box 702, a feedback loop is implemented withwhich the page analysis of units 730, 732, 734 may add new links or URLsto the queue for consideration for inspection in successive operations.Delivery of analysis data to remote in-boxes may be performed for any ofseveral purposes, including distributing the analysis data to otherinstances of the security control computer 120; distributing theanalysis data to a human analyst, for deeper inspection and/orcorrelation to other threats; distributing the analysis data to anintrusion detection system (IDS) or other automated threat analysissoftware, logic or hardware, for deeper inspection and/or correlation toother threats; and/or distributing the analysis data to one or moresensor computers 110 in the field for use in remediation.

3.0 Example Processes of Identifying and Remediating Network SecurityThreats

FIG. 2A illustrates a process of inspecting web pages for securitythreats; FIG. 2B illustrates other aspects of the process of FIG. 2A.The processes of FIG. 2A, FIG. 2B may be implemented using the securitycontrol computer 120 and other elements of FIG. 1, in one embodiment.For example, the inspecting logic 122 may implement the process of FIG.2A, FIG. 2B as described in this section and/or in combination with thefunctional descriptions of the inspecting logic that are provided inother sections. Thus, the flow diagrams of FIG. 2A, FIG. 2B will serveas a functional specification that a skilled person may use to write,debug, execute and otherwise program one or more computer programs,methods, algorithms using any suitable language or programmingenvironment such as JAVA, C++, OBJECTIVE-C, C, PASCAL, or to design thegate structure, layout or programming of ASICS or FPGAs, or other logic,special-purpose computers or general-purpose computers loaded withstored programs.

Referring first to FIG. 2A, in one embodiment, at block 202, the processdetermines a next web page to retrieve. As seen in FIG. 2A, thedetermination at block 202 may be based upon input signals of manykinds, including global user browsing data 200A and ad exchange networkdata 200B received via frontier management unit 201A.

In various embodiments, the global user browsing data 200A may beobtained from third party sources via API calls or request URLs, and mayindicate which web sites and web pages users are browsing on a globalbasis, reputation databases accessible through network requests, orother sources of metadata about security threats, web sites, or webpages. In an embodiment, ad exchange network data 200B may provideadvertisement exchange network data that identifies computers and/orusers based upon the delivery of advertisements through the networks tothose computers, and other sources. Further, which web page to retrievenext may be specified in a request or query from a user computer thatidentifies a particular URL, as seen at block 201B, or based uponscheduling input 201C, as previously described for FIG. 3, FIG. 7. Thus,in various embodiments inspection of pages may occur in real time inimmediate response to a trigger such as user input, ad network data orglobal browsing data, or periodically over time according to a schedule.

In an embodiment, frontier management unit 201A may be configured todetermine a next web page to fetch based upon metadata obtained inrelation to a previously fetched web page. For example, in oneembodiment, frontier management unit 201A may be configured extracting,from a first web page, web page metadata comprising one or more of: aDNS name of a domain of a URL of the web page; an IP address of a webserver that serves the first web page; a URL of the first web page; asource page containing a link that was used to retrieve the first webpage; based upon the web page metadata, determining a plurality ofsecond web pages to fetch and an order of fetching the plurality ofsecond web pages.

At block 204, the process retrieves the next web page from an internetsource such as a web server. At block 206, the process determines a treestructure of the web page; for example, the DOM structure may bedetermined. At block 208, the process stores a representation of thepage structure, excluding page content such as text and images, in adatabase, such as database 140. Block 208 may include storing a hashvalue as an identifier of the web page and/or the structure, and mayinclude storing an XML file specifying the DOM structure. Storing atblock 208 may include skipping pages that have a structure that matchesa template specifying a known bad structure. In other words, ifenrichment sources 150 or local databases 140, 142 indicate that aparticular page structure is already known to be “bad”, then storing thestructure is not necessarily needed.

At block 210, the process requests page reputation data from anenrichment source.

At block 212, the process tests whether the current web page has astructure that is known to be bad based upon the page reputation datathat was retrieved at block 210. If the page structure is known to bebad, then control passes to block 202 at which the next page isprocessed. If the page structure is not known to be bad, then controltransfer to block 214 at which the process tests whether the pagestructure has changed since the last inspection. The test of block 214may include matching a hash value of the web page or its DOM structureto all hash values that are already stored in the database 140, using aSELECT query or other retrieval. If the web page structure has notchanged as tested at block 214, then control passes to block 202 toconsider the next web page; otherwise control transfers to FIG. 2B.

Referring now to FIG. 2B, at block 220, the process examines the webpage to identify features that indicate malware or sources of attacks.Block 220 broadly represents the initiation of an inspection processthat may include the steps of blocks 222, 226, 230, 234 and relatedprocessing, but also may include other operations; for example, block220 could include performing a query to a reputation database based uponthe URL of the web page, or a hash, to retrieve a stored reputationvalue for the web page, URL or domain associated with them.

At block 222, the process reviews each link in the web page. Reviewing alink may comprise programmatically invoking the link, equivalent to auser clicking on the link using a browser.

At block 224, to avoid endless loops caused by link farms in maliciousweb pages, the process computes a score for each redirection path thatis associated with a link, and stores the score. If the score exceeds aspecified threshold so that the link probably would result in thwartingoperation of web pages inspection activities, then output from block 224can mark links or update the databases to prevent traversal of the linksin other inspection operations. For example, if virtually clicking on alink would cause a redirection eight (8) times before reaching anultimate host, then a maliciousness score associated with the link maybe increased or the link may be marked using a binary value indicatingmaliciousness or not to follow the redirections. This approachrecognizes that links are normally not inherently malicious, but maylead a user browser or computer to something that is malicious, so theexistence of loops or multiple redirects is of greater interest than theinherent content of the link or URL.

At block 226, the process inspects each file reference in the web page.Typically file inspection involves executables and ADOBE PORTABLEDOCUMENT FORMAT (PDF) files, which are capable of carrying executablescript code; image files may be ignored, thereby relieving theinspection process of the burden of inspecting a large volume ofinternet content. As part of inspecting a file reference, at block 228,the process determines a status value for the file, such as Known Goodor Known Bad, which may limit or influence other steps.

At block 230, the process determines a reputation score for the web pageas a whole, and at block 232 the database is updated with the reputationscore for the web page as a whole. Block 230 may involve obtainingreputation input from one or more of the enrichment data sources 150.Other attributes pertaining to files may be obtained from enrichmentsources or local databases, including but not limited to certificatechain values, file size, path to the file, etc.

At this point the process optionally may determine an ultimatereputation score for the page as a whole. In one approach, the precedingsteps result in storing various attributes for the page and then theattribute values are fed to a binary circuit decision tree thatdetermines a final result. For example, when the ratio of redirects andIP reputation values are bad, then these two bad results cause followingspecified paths through the binary decision tree and may result in a badlabel. This approach permits determining an ultimate reputation valuefor a page in a very fast manner once the attribute values are availablefrom preceding steps. Further, if the system receives a request forinformation about a particular link, the tree can be run very fast forthe stored attributes of that link to yield a result.

At block 234, the process combines the score with other data, such aslocation data indicating a geographic location of a compromisedcomputer, and performs a remediation analysis. The remediation analysisat block 234 may result in one or more reporting operations at block236, generating graphics or maps at block 238, and/or providing one ormore updates at block 240 to an enterprise firewall, such as firewall113 (FIG. 1). Thus the sensor computers may be used as network queues toalter data flow to the enterprise computers. For example, particulartraffic that the compromised computer is emitting may be blocked. Asother examples, the firewall or compromised computer may be reconfiguredor instructed to drop packets or shoot down packets, disrupt theestablishment of a TCP connection or UDP connection that is partwaythrough handshake negotiation, and/or disrupt or tear down an existingconnection session in the TCP/IP layers or application layers of the OSIreference model.

The operations of block 236, 238 may comprise generating and displayingdata at a user computer or workstation that is coupled to securitycontrol computer 120 for the purpose of trend analysis, geographicanalysis, or other reporting relating to threats. For example, riskreports relating to a particular enterprise computer 112 or compromisedcomputer 106 may be generated that catalog all threats that have beenidentified. Other reports or graphics may indicate total attacks bygeographic location, total attacks of different types by hour, day orother period; total attacks of all types across specified timeintervals; heat maps that show the location of IP addresses known to thesystem with associated score values; risk profiles for an enterpriseorganized by department or other functional unit of the enterprise,based upon a mapping of IP addresses or other computer identifiers tobusiness identifiers of departments or other functional units. Reportscan indicate, for a particular attack, the computers associated with theattack and their locations; details of a file found in a web page thatis associated with an attack; domains related to a domain that hosts thefile and the reputation scores of those domains; files related to thefirst file and reputation or threat values associated with those files.

The techniques described herein offer numerous benefits and significantimprovements over prior approaches or ideas. For example, the systemarchitecture and processes disclosed herein are capable of identifyingmalicious cyber activity outside enterprise networks. As one particularexample, the integration of ad network data can reveal which users of anenterprise, or users of compromised computers, are visiting maliciouswebsites. No software needs to be installed on user systems, such ascompromised computer 106, or in the enterprise, such as on enterprisecomputer 112. The techniques can operate in real time as threatsdevelop, and are content-agnostic in terms of determining reputationscores for files and websites; the content of web pages has no influenceon the reputation scores, and in fact the techniques herein recognizethat the content of malicious web pages often is gibberish, useless, notmeaningful or otherwise has no bearing on whether the DOM structure of apage includes links or file references that are malicious. Theintegration and use of user browsing data obtained from ad deliverynetworks and other sources, to indicate what web pages other users arebrowsing, causes the system herein to be user-driven. That is, thesystem is driven at least in part by actual user browsing behavior, andtherefore the system can inspect and respond to web pages that areactually being browsed, rather than attempting to exhaustively inspectevery page that is available through the public internet with nocorrelation to actual user browsing behavior. Exhaustive inspection canbe performed as a long-term goal based upon available CPU and storageresources, but the integration of actual user browsing behavior data,from data sources such as ad networks that have not been used previouslyfor security analysis, represents a significant advance over prior workin the network security area.

With the foregoing description, the disclosure herein has described thesubject matter of the following numbered clauses:

1. A data processing method providing an improvement in computersecurity, comprising selecting, from a queue identifying a plurality ofweb pages, a particular web page to retrieve from one of a plurality ofinternet sources; causing retrieving a copy of the particular web pagefrom a particular internet source; determining a hierarchical structureof the particular web page; based upon a hierarchical structure of theparticular web page and without consideration of content of theparticular web page, identifying one or more features, of links in theparticular web page or files referenced in the particular web page, thatindicate one or more security threats; determining a reputation scorefor the particular web page; determining a specified remediationmeasure, based upon the reputation score, to remediate a security threatthat is identified in the particular web page; providing the specifiedremediation measure to one or more of a compromised computer, a sensorcomputer and an enterprise computer.

2. The method of clause 1, further comprising reviewing each link in theparticular web page, computing a link score for each redirection pathassociated with that link, and determining the reputation score at leastin part based upon the link score.

3. The method of clause 2, further comprising refraining from using aparticular link to reach another web page referenced in the link whenthe link score is greater than a specified threshold that is associatedwith non-traversable links.

4. The method of clause 1, further comprising inspecting each of thefiles referenced in the particular web page, determining a status valuefor each of the files, and determining the reputation score at least inpart based upon the status value.

5. The method of clause 1, further comprising determining the reputationscore at least in part based upon combining the reputation score withone or more enrichment data sources.

6. The method of clause 1, further comprising determining the reputationscore at least in part based upon combining the reputation score withone or more of geo-location data and one or more other enrichmentsources.

7. The method of clause 1, further comprising performing the selectingbased upon one or more of advertising exchange network bid data andfeedback from analysis of previous web pages.

8. The method of clause 1, further comprising determining the reputationscore for the particular web page, determining the specified remediationmeasure, and providing the specified remediation measure only when thehierarchical structure of the particular web page has not changed sincea last inspection of the same particular web page.

9. The method of clause 1, wherein the steps of the method are performedusing inspecting logic in a security control computer that is coupledthrough one or more networks to a sensor computer that is co-locatedwith and coupled to a compromised computer, and further comprisingproviding the specified remediation measure only to the sensor computer.

10. The method of clause 1, wherein the steps of the method areperformed using inspecting logic in a security control computer that iscoupled through one or more networks to a sensor computer that isco-located with and coupled to a compromised computer that is coupled toa firewall that is configured to control ingress of packets to thecompromised computer, and further comprising providing the specifiedremediation measure only to the firewall.

11. The method of clause 1, wherein the queue is coupled to inspectinglogic that is configured to inspecting logic that is configured to storethe plurality of web pages in the queue based upon input from one ormore of: advertising exchange network bid data; global user browsingdata indicating which web pages are the subject of browsing by aplurality of geographically distributed users; feedback from analysis ofprevious web pages by the inspecting logic; a user query; schedulinginput.

12. A data processing system comprising: a plurality of sensorcomputers, each of which is coupled to different one among a pluralityof compromised computers in geographically distributed locations, eachof the compromised computers comprising at least one malware item thatis configured to direct unauthorized network activity toward one or moreenterprise networks or enterprise computers, wherein the compromisedcomputers are logically between one or more attacker computers and theone or more enterprise networks or enterprise computers; a securitycontrol computer that is coupled to the sensor computers and configuredwith security logic which is configured when executed to perform:obtaining, from the sensor computers, detection data relating to networkmessages that the compromised computers emit, as the compromisedcomputers emit the network messages; using the detection data,identifying one or more security threats that are indicated by thenetwork messages; determining a specified remediation measure toremediate one or more of the security threats; providing the specifiedremediation measure to one or more of the compromised computer, thesensor computer and an enterprise computer.

13. The system of clause 12, further comprising providing the specifiedremediation measure only to the sensor computer, wherein the sensorcomputer is configured, in response to receiving the specifiedremediation measure, to reconfigure a firewall to which the compromisedcomputer is coupled using firewall instructions that are based upon thespecified remediation measure.

14. The system of clause 12, further comprising, based upon thedetection data, creating and causing displaying, in a user interface ofa computer display device, one or more reports specifying a plurality ofattacks directed toward the enterprise network or enterprise computer.

15. The system of clause 12, further comprising: obtaining, from one ormore enrichment services, based upon network addresses in the networkmessages, geo-location data indicating a particular geographic location;creating and causing displaying, in the user interface, an aggregatenumber of attackers in the particular geographic location that haveinitiated attacks toward the enterprise network or enterprise computer.

16. The system of clause 12, further comprising: receiving, from one ormore advertising exchange networks, advertising presentation dataindicating presentations of advertisements to particular browsers thathave browsed to particular websites; determining, based upon thedetection data, whether the particular websites are associated withnetwork attacks and/or malware; in response to the determining, storingtransit data specifying computers that have visited the particularwebsites and using the transit data to determine a plurality ofparticular web pages to inspect for threats.

17. The system of clause 12, further comprising: using the sensorcomputer, selecting one or more of the network messages emitted from thecompromised computer and directed toward the enterprise computer;queuing the selected one or more of the network messages in queues atthe sensor computer; inspecting and modifying the queued one or morenetwork messages to remove one or more security threats beforeforwarding the queued network messages to the enterprise computer.

18. The system of clause 17 wherein the selection comprises filteringthe one or more network messages emitted from the compromised computerbased upon one or more ports of interest.

19. The system of clause 17 wherein the selection comprises selectingall network messages when a total message output or packet output of thecompromised computer exceeds one or more specified thresholds.

20. The system of clause 12, wherein the security control computerfurther comprises inspecting logic that is configured to perform:selecting, from a queue identifying a plurality of web pages, aparticular web page to retrieve from one of a plurality of internetsources; causing retrieving a copy of the particular web page from aparticular internet source; determining a hierarchical structure of theparticular web page; based upon a hierarchical structure of theparticular web page and without consideration of content of theparticular web page, identifying one or more features, of links in theparticular web page or files referenced in the particular web page, thatindicate one or more security threats; determining a reputation scorefor the particular web page; determining a specified remediationmeasure, based upon the reputation score, to remediate a security threatthat is identified in the particular web page; providing the specifiedremediation measure to one or more of the compromised computer, thesensor computer and the enterprise computer.

21. The system of clause 20, wherein the inspecting logic is furtherconfigured to review each link in the particular web page, compute alink score for each redirection path associated with that link, anddetermine the reputation score at least in part based upon the linkscore.

22. The system of clause 21, wherein the inspecting logic is furtherconfigured to refrain from using a particular link to reach another webpage referenced in the link when the link score is greater than aspecified threshold that is associated with non-traversable links.

23. The system of clause 20, wherein the inspecting logic is furtherconfigured to inspect each of the files referenced in the particular webpage, determine a status value for each of the files, and determine thereputation score at least in part based upon the status value.

24. The system of clause 20, wherein the inspecting logic is furtherconfigured to determine the reputation score at least in part based uponcombining the reputation score with one or more enrichment data sources.

25. The system of clause 20, wherein the inspecting logic is furtherconfigured to determine the reputation score at least in part based uponcombining the reputation score with one or more of geo-location data andone or more other enrichment sources.

26. The system of clause 20, wherein the inspecting logic is furtherconfigured to perform the selecting based upon one or more ofadvertising exchange network bid data and feedback from analysis ofprevious web pages.

27. The system of clause 20, wherein the inspecting logic is furtherconfigured to determine the reputation score for the particular webpage, determine the specified remediation measure, and provide thespecified remediation measure only when the hierarchical structure ofthe particular web page has not changed since a last inspection of thesame particular web page.

28. The system of clause 20, wherein the inspecting logic is configuredto store the plurality of web pages in the queue based upon input fromone or more of: advertising exchange network bid data; global userbrowsing data indicating which web pages are the subject of browsing bya plurality of geographically distributed users; feedback from analysisof previous web pages by the inspecting logic; a user query; schedulinginput.

4.0 Implementation Mechanisms—Hardware Overview

According to one embodiment, the techniques described herein areimplemented by one or more special-purpose computing devices. Thespecial-purpose computing devices may be hard-wired to perform thetechniques, or may include digital electronic devices such as one ormore application-specific integrated circuits (ASICs) or fieldprogrammable gate arrays (FPGAs) that are persistently programmed toperform the techniques, or may include one or more general purposehardware processors programmed to perform the techniques pursuant toprogram instructions in firmware, memory, other storage, or acombination. Such special-purpose computing devices may also combinecustom hard-wired logic, ASICs, or FPGAs with custom programming toaccomplish the techniques. The special-purpose computing devices may bedesktop computer systems, portable computer systems, handheld devices,networking devices or any other device that incorporates hard-wiredand/or program logic to implement the techniques.

For example, FIG. 5 is a block diagram that illustrates a computersystem 500 upon which an embodiment of the invention may be implemented.Computer system 500 includes a bus 502 or other communication mechanismfor communicating information, and a hardware processor 504 coupled withbus 502 for processing information. Hardware processor 504 may be, forexample, a general purpose microprocessor.

Computer system 500 also includes a main memory 506, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 502for storing information and instructions to be executed by processor504. Main memory 506 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by processor 504. Such instructions, when stored innon-transitory storage media accessible to processor 504, rendercomputer system 500 into a special-purpose machine that is customized toperform the operations specified in the instructions.

Computer system 500 further includes a read only memory (ROM) 508 orother static storage device coupled to bus 502 for storing staticinformation and instructions for processor 504. A storage device 510,such as a magnetic disk or optical disk, is provided and coupled to bus502 for storing information and instructions.

Computer system 500 may be coupled via bus 502 to a display 512, such asa cathode ray tube (CRT), for displaying information to a computer user.An input device 514, including alphanumeric and other keys, is coupledto bus 502 for communicating information and command selections toprocessor 504. Another type of user input device is cursor control 516,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to processor 504 and forcontrolling cursor movement on display 512. This input device typicallyhas two degrees of freedom in two axes, a first axis (e.g., x) and asecond axis (e.g., y), that allows the device to specify positions in aplane.

Computer system 500 may implement the techniques described herein usingcustomized hard-wired logic, one or more ASICs or FPGAs, firmware and/orprogram logic which in combination with the computer system causes orprograms computer system 500 to be a special-purpose machine. Accordingto one embodiment, the techniques herein are performed by computersystem 500 in response to processor 504 executing one or more sequencesof one or more instructions contained in main memory 506. Suchinstructions may be read into main memory 506 from another storagemedium, such as storage device 510. Execution of the sequences ofinstructions contained in main memory 506 causes processor 504 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “storage media” as used herein refers to any non-transitorymedia that store data and/or instructions that cause a machine tooperation in a specific fashion. Such storage media may comprisenon-volatile media and/or volatile media. Non-volatile media includes,for example, optical or magnetic disks, such as storage device 510.Volatile media includes dynamic memory, such as main memory 506. Commonforms of storage media include, for example, a floppy disk, a flexibledisk, hard disk, solid state drive, magnetic tape, or any other magneticdata storage medium, a CD-ROM, any other optical data storage medium,any physical medium with patterns of holes, a RAM, a PROM, and EPROM, aFLASH-EPROM, NVRAM, any other memory chip or cartridge.

Storage media is distinct from but may be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that comprise bus 502. Transmission media can also take the formof acoustic or light waves, such as those generated during radio-waveand infra-red data communications.

Various forms of media may be involved in carrying one or more sequencesof one or more instructions to processor 504 for execution. For example,the instructions may initially be carried on a magnetic disk or solidstate drive of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 500 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 502. Bus 502 carries the data tomain memory 506, from which processor 504 retrieves and executes theinstructions. The instructions received by main memory 506 mayoptionally be stored on storage device 510 either before or afterexecution by processor 504.

Computer system 500 also includes a communication interface 518 coupledto bus 502. Communication interface 518 provides a two-way datacommunication coupling to a network link 520 that is connected to alocal network 522. For example, communication interface 518 may be anintegrated services digital network (ISDN) card, cable modem, satellitemodem, or a modem to provide a data communication connection to acorresponding type of telephone line. As another example, communicationinterface 518 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, communication interface 518sends and receives electrical, electromagnetic or optical signals thatcarry digital data streams representing various types of information.

Network link 520 typically provides data communication through one ormore networks to other data devices. For example, network link 520 mayprovide a connection through local network 522 to a host computer 524 orto data equipment operated by an Internet Service Provider (ISP) 526.ISP 526 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 528. Local network 522 and Internet 528 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 520and through communication interface 518, which carry the digital data toand from computer system 500, are example forms of transmission media.

Computer system 500 can send messages and receive data, includingprogram code, through the network(s), network link 520 and communicationinterface 518. In the Internet example, a server 530 might transmit arequested code for an application program through Internet 528, ISP 526,local network 522 and communication interface 518.

The received code may be executed by processor 504 as it is received,and/or stored in storage device 510, or other non-volatile storage forlater execution.

5.0 Remediation of Security Threats

Various remediation measures can be implemented by, for example, thesensor computer 110. The sensor computer 110 can generate and send anaction packet to the compromised computer 106 that terminates anestablished communication connection or attempted communicationconnection between the compromised computer 106 and the enterprisecomputer 112. In an embodiment, sensor computer 110, via a network tapconfiguration, receives communication packets sent by the compromisedcomputer 106. The sensor computer 110 determines whether an enterprisecomputer 112 is targeted by the compromised computer 106. If anenterprise computer 112 is the target, then the sensor computer 110generates an action packet that appears to be from the enterprisecomputer 112 and that causes connection between the compromised computer106 and the enterprise computer 112 to be slowed or stopped. The actionpacket appears to be from the enterprise computer 112 by virtue ofhaving header fields that match those of the communication packet sentby the compromised computer 106. Specifically, because the sensorcomputer 110 is co-located with the compromised computer 106, TCP/IP orUDP headers in packets sent by the compromised computer 106 can beaccessed and duplicated by the sensor computer 110.

FIG. 8 illustrates a computer networking environment featuring a sensorcomputer 110 co-located with a compromised computer 106. The compromisedcomputer 106 has a public IP address and is in communication with anenterprise computer 112. As depicted in the environment of FIG. 1, thesensor computer 110 and the compromised computer 106 can be logicallybehind a firewall such as the firewall 109 of FIG. 1. In some instances,a TCP/IP or UDP connection is in the process of reaching the establishedstate through a handshake negotiation or has been established betweenthe compromised computer 106 and the enterprise computer 112.

In an embodiment, sensor computer 110 comprises a packet processing unit(PPU) 802, an indicator list unit (ILU) 804, and a rapid dispatcher unit(RDU) 806. The PPU 802 is configured to receive, via a network tapconfiguration, copies of packets sent by the compromised computer 106.The network tap can include the interface tap logic 304 of FIG. 3. Anexample embodiment of a network tap is depicted in FIG. 9. The shownnetwork tap comprises hardware components such as a switch 902 and arouter 904. FIG. 9 further depicts the sensor computer 110 beingco-located with the compromised computer 106 by virtue of positioningthe network tap logically between the compromised computer 106 and theInternet.

Returning to FIG. 8, the PPU 802 reads the headers of the packets orsegments received from the compromised computer 106 via the network tap.By virtue of being co-located with the compromised computer 106, theheader fields of the sent packets are visible to the sensor computer110. The headers are read to identify an IP address of a target computerto which the packet or segment is sent. The PPU 802 generates a querywith the IP address of the target computer and sends the query to theILU 804.

Upon receiving the query, the ILU 804 determines whether target computeris one of a plurality of enterprise computers that includes theenterprise computer 112. The ILU 804 compares the IP address included inthe query to IP addresses of the plurality of enterprise computers. TheIP addresses of the plurality of enterprise computers are stored in adata structure at the sensor computer 110 or at another computer, suchas the security control computer 120 or in the database 140 and/or 142of FIG. 1. Any of several kinds of data structures can be used to storethe IP addresses of the plurality of enterprise computers, including butnot limited to, arrays, hash tables, and sets. In other embodiments, theintended recipient of the sent data packet can be identified usingidentifiers or descriptors other than an IP address.

If the target computer to which the packet or segment is sent is not oneof the plurality of enterprise computers (e.g., the enterprise computer112), then the ILU 804 instructs the sensor computer 110 to take nofurther action, allowing the compromised computer 106 to communicatefreely with the target computer.

If the target computer to which the packet or segment is sent is one ofthe plurality of enterprise computers (e.g., the enterprise computer112), then the ILU 804 is configured to generate and send an actionrequest instructing the RDU 806 to generate an action packet.

The RDU 806 is configured to generate an action packet and send theaction packet to the compromised computer 106. The action packet, whenreceived and processed by the compromised computer 106, causes thecompromised computer 106 to stop or slow communication with theenterprise computer 112 via one or more remediation measures.

The action packet is a TCP or UDP packet or segment and can have aheader and a payload. The header of the action packet is generated byduplicating fields from the communication packet sent by the compromisedcomputer 106. Thus, the action packet appears to have been sent by theenterprise computer 112 in response to the communication packet. Theenterprise computer 112 can still receive the communication packet but,because the compromised computer 106 receives and processes an actionpacket from the sensor computer 110, the compromised computer 106 doesnot send subsequent packets to the enterprise computer 112.

Examples of remediation measures involve modifying some fields in theheader of the action packet to cause a three-way handshake to initiate aTCP connection to fail. The three-way handshake is initiated byenterprise computer 112 once the compromised computer 106 has a passiveopen connection at the enterprise computer 112. The enterprise computer112 completes the three-way handshake by sending an ACK segment to thecompromised computer 106 in response to a SYN-ACK segment received fromthe compromised computer 106.

In some embodiments, the sensor computer 110 receives the SYN-ACKsegment via the network tap. The RDU 806 generates action packet, andspecifically, an RST segment by duplicating some of the header field sothat the RST segment appears to have been sent by the enterprisecomputer 112. The RST segment causes the compromised computer 106 toreset the connection.

In some instances, however, the RST segment will be interpreted as a“spurious reset” by the compromised computer 106, causing thecompromised computer 106 to disregard the RST segment in implementationsthat conform to the standard TCP protocol specification. To prevent thecompromised computer 106 from disregarding the action packet, instead ofan RST segment, in an embodiment, the action packet sent can include anACK segment having an unexpected sequence number, which may be termed asa “bogus ACK”. The unexpected sequence number is out-of-sequencerelative to a sequence number that was sent in a SYN segment in thebeginning of the three-way handshake; that is, the sequence number isout-of-sequence in relation to past sequence numbers that have been senton the connection. The unexpected sequence number is, in some instances,less than the sequence number included in the SYN segment and greaterthan a sequence number included in a previous ACK segment.

In some instances, the action packet is an ACK segment having a FIN bitset. The set FIN bit causes the compromised computer 106 to close theTCP connection with the enterprise computer 112.

In other instances, a duplicate ACK can be sent to the compromisedcomputer 106 during the three-way handshake. The duplicate can effect areset of the connection. If the duplicate ACK is sent after theconnection is established, its receipt by the compromised computer 106can trigger error handling protocols that slow communication with theenterprise computer 112.

In embodiments where a TCP connection between the compromised computer106 and the enterprise computer 112 is already in the ESTABLISHED state,the header of the action packet can be generated to include a sequencenumber that is out-of-sequence in relation to the TCP connection.

In some embodiments, the header of the action packet is populatednormally but the payload of the packet is generated in a way that willdisrupt a TCP connection or UDP connection. UDP connections often areused for streaming content or for Voice Over IP (VOIP) content. In someembodiments, the generated payload of the action packet is a duplicateof a previously sent packet. In other embodiments, the generated payloadcomprises munged data generated by transforming a payload of thecommunication packet. The duplicate and munged payloads can effectivelyrender the data received by the compromised computer 106 unreadable.

In some embodiments, the sensor computer 110 can detect a domain nameservice (DNS) query sent by the compromised computer 106. The PPU 802reads the domain name in the DNS query and sends a query to the ILU 804including the domain name in the DNS query. If the domain name is thedomain name of the enterprise computer 112, then the ILU 804 generatesand sends an action request to the RDU 806. The RDU 806 generates anaction packet using duplicated fields from the DNS query that appears tothe compromised computer 106 to be a DNS reply from a DNS server. Incontrast to an actual DNS reply, the action packet generated by the RDU806 can include an invalid IP address.

FIG. 10 illustrates a process of remediation of security threats. Theprocess can be performed by the sensor computer 110.

In an operation 1002, a communication packet sent by the compromisedcomputer 106 to a target computer is received via a network tap at thesensor computer 110. As discussed above, the communication packet canstill be received by the target computer (e.g., the enterprise computer112). The operation 1002 can be performed by, for example, the PPU 802.

In an operation 1004, the header fields of the received packet are read.The contents of the TCP packet or segment is visible to the sensorcomputer 110 at least because the sensor computer 110 is co-located withthe compromised computer 106. From the read packet, the IP address ofthe target computer is determined. The operation 1004 can be performedby the PPU 802.

In an operation 1006, the IP address read from the receivedcommunication packet is queried. In some instances, the IP address iscompared to IP addresses of enterprise computers, including theenterprise computer 112. The operation 1006 can be performed by, forexample, the ILU 804.

In an operation 1008, a determination is made as to whether the IPaddress matches any of the IP addresses of the enterprise computers. Thedetermination can be made by the ILU 804. If it is determined that thereis no match, the process of FIG. 10 starts over with the operation 1002.

If, however, it is determined that there is a match, in an operation1010, an action request is generated. The action request includes aninstruction to generate an action packet as a remediation measure. Theoperation 1010 can be performed by the ILU 804.

In an operation 1012, an action packet is generated that includes atleast some of the header fields read from the communication packet. Theaction packet is generated so as to cause the compromised computer 106to abort an attempt to establish a connection with the enterprisecomputer 112, to disconnect an established connection between thecompromised computer 106 and the enterprise computer 112, or to slowcommunication between the compromised computer 106 and the enterprisecomputer 112. In some embodiments, the action packet can be sent to thefirewall 109 or the enterprise computer 112 and effect similar results.Particular remedial measures that can be used are described above.

6.0 Other Aspects of Disclosure

Using the networked computer arrangements, intermediary computer, and/orprocessing methods described herein, security in client-server dataprocessing may be significantly increased.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. The sole and exclusive indicator of the scope of the invention,and what is intended by the applicants to be the scope of the invention,is the literal and equivalent scope of the set of claims that issue fromthis application, in the specific form in which such claims issue,including any subsequent correction.

What is claimed is:
 1. A method comprising: receiving, using a networktap of a sensor computer that is coupled to and co-located with acompromised computer that hosts or executes malware, a communicationpacket that was sent from the compromised computer to a target computerand allowed to pass to the target computer; reading, at the sensorcomputer, a plurality of fields within a header of the communicationpacket; determining, at the sensor computer, that the communicationpacket is sent as part of a potential malware attack on the targetcomputer; generating, using the sensor computer, an action packet havinga header, which includes duplicates of at least some fields of theplurality of fields so as to appear to be generated by the targetcomputer, and a payload; and sending the action packet to thecompromised computer, wherein the action packet is configured, whenreceived by the compromised computer, to cause the compromised computerto terminate an established communication connection between thecompromised computer and the target computer.
 2. The method of claim 1,further comprising determining that the communication packet is sent aspart of a potential malware attack on the target computer by determiningthat the compromised computer is initiating a Denial of Service (DoS)attack.
 3. The method of claim 1, further comprising determining thatthe communication packet is sent as part of a potential malware attackon the target computer by determining that the compromised computer isinitiating an installation of viruses, spam, or adware on the targetcomputer.
 4. The method of claim 1, further comprising determining thatthe communication packet is sent as part of a potential malware attackon the target computer by determining that the compromised computer isinitiating password harvesting on the target computer.
 5. The method ofclaim 1, wherein the action packet is configured, when received by thecompromised computer, causes the compromised computer to terminate anattempted communication connection between the compromised computer andthe target computer.
 6. The method of claim 1, wherein the sensorcomputer receives the communication packet via a firewall that logicallyseparates the sensor computer and the compromised computer from theInternet.
 7. The method of claim 1, further comprising determining, atthe sensor computer, that the communication packet is sent as part of apotential malware attack on the target computer by identifying an IPaddress of the target computer.
 8. The method of claim 1, wherein theaction packet is configured to cause the compromised computer to disrupta transmission control protocol (TCP) connection or a User DatagramProtocol (UDP) connection.
 9. The method of claim 1, further comprisingdetermining that the communication packet is sent as part of a potentialmalware attack on the target computer by detecting a domain name service(DNS) query sent by the compromised computer and wherein the actionpacket appears to the compromised computer to be a DNS reply from a DNSserver and includes an invalid IP address.
 10. A computer systemproviding an improvement in remediating malware attacks in computersecurity, comprising: one or more processors; a non-transitorycomputer-readable storage medium having instructions embodied thereon,which, when executed by the one or more processors, cause: receiving,using a network tap of a sensor computer that is coupled to andco-located with a compromised computer that hosts or executes malware, acommunication packet that was sent from the compromised computer to atarget computer and allowed to pass to the target computer; reading, atthe sensor computer, a plurality of fields within a header of thecommunication packet; determining, at the sensor computer, that thecommunication packet is sent as part of a potential malware attack onthe target computer; generating, using the sensor computer, an actionpacket having a header, which includes duplicates of at least somefields of the plurality of fields so as to appear to be generated by thetarget computer, and a payload; and sending the action packet to thecompromised computer, wherein the action packet is configured, whenreceived by the compromised computer, to cause the compromised computerto terminate an established communication connection between thecompromised computer and the target computer.
 11. The computer system ofclaim 10 further comprising instructions which when executed causedetermining that the communication packet is sent as part of a potentialmalware attack on the target computer by determining that thecompromised computer is initiating a Denial of Service (DoS) attack. 12.The computer system of claim 10 further comprising instructions whichwhen executed cause determining that the communication packet is sent aspart of a potential malware attack on the target computer by determiningthat the compromised computer is initiating an installation of viruses,spam, or adware on the target computer.
 13. The computer system of claim10 further comprising instructions which when executed cause determiningthat the communication packet is sent as part of a potential malwareattack on the target computer by determining that the compromisedcomputer is initiating password harvesting on the target computer. 14.The computer system of claim 10 wherein the action packet is configured,when received by the compromised computer, to cause the compromisedcomputer to terminate an attempted communication connection between thecompromised computer and the target computer.
 15. The computer system ofclaim 10 wherein the sensor computer and the compromised computer arelogically separated from the Internet via a firewall.
 16. The computersystem of claim 10 further comprising instructions which when executedcause determining, at the sensor computer, that the communication packetis sent as part of a potential malware attack on the target computerfurther cause identifying an IP address of the target computer.
 17. Thecomputer system of claim 10 further comprising instructions which whenexecuted cause the compromised computer to disrupt a transmissioncontrol protocol (TCP) connection or a User Datagram Protocol (UDP)connection.
 18. The computer system of claim 10 further comprisinginstructions which when executed cause determining that thecommunication packet is sent as part of a potential malware attack onthe target computer by detecting a domain name service (DNS) query sentby the compromised computer and wherein the action packet appears to thecompromised computer to be a DNS reply from a DNS server and includes aninvalid IP address.
 19. A non-transitory computer-readable storagemedium storing one or more instructions which, when executed by one ormore processors, cause the one or more processors to perform a method,the method comprising: receiving, using a network tap of a sensorcomputer that is coupled to and co-located with a compromised computerthat hosts or executes malware, a communication packet that was sentfrom the compromised computer to a target computer and allowed to passto the target computer; reading, at the sensor computer, a plurality offields within a header of the communication packet; determining, at thesensor computer, that the communication packet is sent as part of apotential malware attack on the target computer; generating, using thesensor computer, an action packet having a header, which includesduplicates of at least some fields of the plurality of fields so as toappear to be generated by the target computer, and a payload; andsending the action packet to the compromised computer, wherein theaction packet is configured, when received by the compromised computer,to cause the compromised computer to terminate an establishedcommunication connection between the compromised computer and the targetcomputer.
 20. The non-transitory computer-readable storage medium ofclaim 17, the method further comprising determining that thecommunication packet is sent as part of a potential malware attack onthe target computer by determining that the compromised computer isinitiating a Denial of Service (DoS) attack.